ILC08 Chicago November 2008 Summary of Recent Results from SLAC M. Pivi, J. Ng, D. Arnett, G. Collet, T. Markiewicz, D. Kharakh, R. Kirby, F. Cooper, C. Spencer, B. Kuekan, J. Seeman, P. Bellomo, J.J. Lipari, J. Olzewski, L. Wang, T. Raubenheimer (SLAC) C. Celata, M. Furman (LBNL) ILC08 Chicago, University of Illinois November 2008

ILC08 Chicago November 2008 R&D work at SLAC on mitigation techniques Installed 3 experiments with test chambers in PEP-II: –“ECLOUD1” to monitor the reduction in-situ of the Secondary Electron Yield (SEY) due to “conditioning” –“ECLOUD2” to test Groove mitigation –“ECLOUD3” chicane to test e-cloud in magnetic field: Aluminum and TiN coated chambers

ILC08 Chicago November 2008 ECLOUD1: SEY station 1.5% of the ring Electron cloud chambers installed in PEP-II ILC tests - SLAC ECLOUD2: grooves tests ECLOUD3: Al uncoated and TiN-coated chamber in chicane

ILC08 Chicago November 2008 “ECLOUD1” SEY test station in PEP-II Transfer system at 0 o PEP-II LER e+  Transfer system at 45 o 2 samples facing beam pipe are irradiated by SR Isolation valves ILC tests, M. Pivi et al. – SLAC

ILC08 Chicago November 2008 Results of Conditioning in PEP-II LER beam line TiN samples measured before and after 2-months conditioning in the beam line. Samples inserted respectively in the plane of the synchrotron radiation fan (0 o position) and out (45 o ). ILC tests, M. Pivi et al. – SLAC Before installation in beam line After conditioning e- dose > 40mC/mm**2 Similar SEY measured in situ at KEKB by S. Kato et al.

ILC08 Chicago November 2008 TiN surface standing-by in vacuum: SEY < 1 even after 1000 hours. Recontamination effects are small for TiN after conditioning in PEP-II. Secondary Electron Yield recontamination after long term exposure in vacuum environment

ILC08 Chicago November 2008 ECLOUD1: Uncoated Aluminum in PEP-II After long conditioning in PEP-II beam line: sample SEY maximum remains > 2 Well supported by previous SLAC and CERN set-up measurements CesrTA / Daphne have aluminum vacuum chambers: expect large e-cloud effects M. Pivi, R. Kirby – SLAC

ILC08 Chicago November 2008 SEY before installation SEY after conditioning TiN/Al TiZrV Cu StSt Al Summary “ECLOUD1” experiment Summary of samples conditioned in the accelerator beam line References: – papers in preparation for submission to Physical Review ST AB and Phys. Rev. Lett. – M. Pivi et al. MOPP064 EPAC 2008; – F. Le Pimpec et al. Nucl. Inst. and Meth., A564 (2006) 44; – F. Le Pimpec et al. Nucl. Inst. and Meth., A551 (2005) 187;

ILC08 Chicago November 2008 “ECLOUD3”: Layout of PEP-II dedicated Chicane LER HER PEP-II

ILC08 Chicago November 2008 “ECLOUD3” Chicane: Vacuum Chambers Layout 2 chambers: 135.3” and 31.2”. 4 analyzer electron cloud detectors, one at each magnet location The Al chamber is partially coated with TiN Aluminum TiN coating on Al Spool (Groove)

ILC08 Chicago November 2008

ILC08 Chicago November 2008

ILC08 Chicago November 2008 Electron detectors Dipole iron plates e+e+ Al and TiN test chamber

ILC08 Chicago November 2008 Plan of ECLOUD3 experiments in PEP-II Measurements plan: Electron cloud current as a function of beam current Electron energy spectrum Verify existence of resonances in electron cloud density as suggested by C. Celata LBNL for Aluminum and TiN coating chamber

ILC08 Chicago November 2008 Electron cloud detectors in magnets, SLAC Electron detectors, Retarding Field Analyzer (RFA) type [R. Rosenberg, K. Harkay] M. Pivi and R. Kirby, SLAC 17 collectors to measure horizontal e- distribution and 3 grids to measure e- energy spectrum Beam direction

ILC08 Chicago November 2008 Electron cloud with no field: Chicane OFF Electron collectors signal in the two sections with no magnetic field. TiN coating (below) shows a reduction of a factor ~30 with respect to Aluminum (above).

ILC08 Chicago November 2008 Electron cloud in a dipole field: Chicane ON Uncoated Aluminum section L. Wang et al, SLAC TiN-coated section Note the magnitude of reduction in TiN section. Distributions consistent with simulation. “Two-stripe” electron distribution in the horizontal plane Horizontal plane

ILC08 Chicago November 2008 Electron energy spectrum Integrated and differential spectra: sum of all channels.Differential energy spectra for each RFA channel. Retarding Field Analyzers: Grid used to repel electrons and measure energy spectrum Consistent with previous simulations. [L. Wang, ECLOUD04, SLAC-PUB-10751] J. Ng et al, SLAC

ILC08 Chicago November 2008 ECLOUD3: Magnetic field Resonances e- cyclotron period and bunch spacing couple into resonances n proportional to B field. We varied chicane magnetic field. Electron flux peaks (and valleys) separated by integer values of n. Phase of cyclotron motion with respect to bunch crossing affects energy gain, possibly leading to the observed modulation in electron flux at the chamber wall. M. Pivi, J. Ng et al, SLAC

ILC08 Chicago November 2008 Observed in simulations by C. Celata LBNL

ILC08 Chicago November 2008 Resonance effect in a dipole field: Aluminum section Uncoated aluminum section. Electron cloud current signal as a function of the ratio n, cyclotron period to bunch spacing, at 2500 mA PEP-II LER beam current. The first five plots are data from individual RFA collector stripes. The bottom plot shows the total signal summed over all collectors peaks at n=half integer. J. Ng et al, SLAC NOTE: far from center chamber axis (large x’s), the e- signal peaks at n=integer NOTE: close to center axis, a stronger signal peaks at n=half integer

ILC08 Chicago November 2008 Resonance effect in a dipole field: TiN section Same as previous slide but for TiN coated section The first five plots are data from individual RFA collector stripes. The bottom plot shows the total signal summed over all collectors peaks at (large) n=integer values. J. Ng et al, SLAC NOTE: orders of magnitude lower current than aluminum section. NOTE: peaks.

ILC08 Chicago November 2008 ECLOUD3: Summary Goal: mitigation of electron clouds in a dipole magnetic field region Results: –Demonstrated TiN-coating is very effective in a dipole –Characterized electron cloud in DR dipole field –Observed new resonance: modulation in electron flux as magnetic field strength is varied –Resonance: reduce electron cloud density in ILC DR by tuning the arc dipole field References: –paper being prepared for submission to Phys. Rev. Lett. –M. Pivi, J. Ng et al., EPAC 2008;

Additional Plans *KEK: –Ongoing tests of SLAC groove insertions in wigglers at KEKB (see Suetsugu-san presentations). *CERN: manufacturing small groove insertions for SPS dipole tests. *CesrTA: –Removed all PEP-II experiments ECLOUD1,2,3 (plus additional grooved chamber) and redeploying at Cornell. *Project-X: –Re-deploy ECLOUD1 (SEY Station) to Fermilab (after CesrTA)

ILC GDE - ILCDR08 Cornell November 2008 Milestones to ILC Technical Design Phase Characterize the electron cloud build-up and instability by simulations and measurements in existing accelerators: CesrTA, SPS, Daphne, SuperKEKB Model the ILC DR electron cloud instability Characterize Photoemission in ILC DR parameters range (experimental) Evaluate need for additional mitigation techniques (besides coating): Clearing electrodes Triangular groove Antechamber Characterize the impedance and HOMs of mitigation techniques Specify mitigation requirements for DR The goal is to complete the following tasks by 2010 as input for the Technical Design Phase:

ILCDR08, Cornell November 2008 Recommendation for mitigation for ILC DR design: Under Discussion DR element% ringAntechamberCoatingAdditional Mitigation Remarks DRIFT in STRAIGHT 33NoNEGSolenoidGroove if necessary DRIFT in ARC 56Downstream of BEND only NEGSolenoidGroove if necessary BEND7YesTiNGrooves and Electrodes WIGG3YesTiNElectrodes and Grooves QUAD1Downstream BEND / WIGG TiNGrooves and Electrodes Preliminary table to be completed as input for Technical Design Phase. Goal is to turn all Red colors to Green in the next two years. Other mitigations under development (ex: Carbon coating CERN)

Summary *Successful international R&D program on electron cloud mitigations. *TiN coating has been demonstrated to have an SEY below the instability threshold. Work continues to address a few remaining issues. *Yet, requirements at future colliders (2 picometer emittance in the ILC DR, e.g.) are challenging. *Hence, close collaboration between labs to develop complementary mitigation techniques is needed to further suppress the electron cloud effect. M. Pivi, SLAC November 2008, ILC08.